orpiment (n.)

"arsenic trisulphide," a bright yellow mineral substance used in dyeing as a pigment and also medicinally and for destroying lice, late 13c., orpyment, from Old French orpiment "arsenic trisulphide, yellow color," from Latin auripigmentum, from aurum "gold" (see aureate) + pigmentum "coloring matter, pigment, paint," from stem of pingere "to color, paint," from a nasalized form of PIE root *peig- "to cut, mark by incision."